Many automated blood pressure monitors employ an inflatable cuff to exert controlled counterpressure on the vasculature of the subject. One large class of such monitors, exemplified by that described in U.S. Pat. Nos. 4,349,034 and 4,360,029, both to Maynard Ramsey, III and commonly assigned herewith, employs the oscillometric methodology. In accordance with this method, a pneumatic cuff is inflated to a pressure which substantially blocks an artery, such as the brachial artery, and then is progressively relaxed, i.e., stepwise. Heart contractions produce blood pressure pulsations which produce oscillations in blood pressure cuff pressure at the point of occlusion. and the amplitudes of these oscillations are measured and processed to determine mean arterial pressure, systolic pressure, and diastolic pressure.
In some variants of oscillometric systems, the cuff pressure is continuously bled, typically in linear fashion, rather than being relaxed in predetermined decrements. Typically in both, however, cuff pressure is established by a pump mechanism which, under electronic or computer control, is activated at the initiation of the measurement cycle to inflate the cuff. Thereafter, the cuff is deflated with the aid of selectively actuated pressure venting valves. Clearly, such systems place great reliance on the speed, accuracy, and reliability of such a pump. Even the best and fastest commercial pumping apparatus may require in the range of 5-10 seconds for the pump to establish a desired cuff pressure (e.g. 3 to 4 psi) prior to initiation of the depressurization and measurement cycle. In a measurement cycle taking 20-30 seconds by itself, the additional time required for inflation, being non data-productive, constitutes a wasteful interlude.
Instead of inflating initially to above systolic pressure followed by a deflation sequence during which measurements are taken, systems are also known that interrupt the initial rapid inflation at a point below diastolic pressure, with controlled further inflation to above systolic, measurements being taken during the controlled further inflation phase.
It is, accordingly, a primary object of the present invention to reduce the overall blood pressure measurement time by reducing the time required for cuff inflation at the initiation of each cycle.
The proliferation of apparatus available in the critical care unit, intensive care unit, or operating theatre has placed a premium on space. It is, therefore, desirable either to minimize the space occupied by blood pressure apparatus, or at the least, while functionally improving the monitors, to avoid increasing the space allocation necessary for the monitors. Likewise, portability of monitors suggests reduction of the overall size of the apparatus.
It is therefore another object of the present invention to provide accelerated inflation while maintaining or decreasing the overall size of the monitor. It is a further object to provide compact, effective inflation apparatus with a reduced power, accuracy, and speed burden on the pump.
Another disadvantage found in presently available automatic monitoring apparatus of the foregoing type is the disturbing noise level produced by the air pump when operating. Therefore, it is yet another object of the present invention to produce an apparatus wherein the noise produced by the pump is substantially confined within the apparatus.